Quenching device

The rapid-quenching device employed will be described in Chapter 5. A polished cylindrical steel specimen, 11.28 mm diameter and 5 mm high, was held in a liquid aluminium alloy (volume 10 cm ) protected by a flux for 100 to 3600 s, and then the solid specimen together with the melt were rapidly cooled by quenching in water to arrest the reactions at the steel-aluminium interface. The time of cooling from 700°C down to room temperature did not exceed 2 s. The bimetallic specimen thus obtained was... 

The process of dissolution of a solid in a liquid can readily be investigated using a rapid-quenching device like that shown schematically in Fig. 5.3. Depending on the nature of substances to be studied, this may be carried out either in vacuum, or in a protective atmosphere (inert gases, hydrogen, nitrogen, etc), or under a flux.197,303309... 

Fig. 5.3. Rapid-quenching device for investigating the process of dissolution of a solid in a liquid by the rotating disc method.309 1, electric-resistance furnace 2, solid specimen 3, protective tube 4, electric motor 5, rotating shaft 6, stopper 7, thermocouple 8, flux 9, liquid.

Figure 4 A schematic representation of the experimentai approach for time-resoived XAS measurements. XAS provides local structural and electronic information about the nearest coordination environment surrounding the catalytic metal ion within the active site of a metalloprotein in solution. Spectral analysis of the various spectral regions yields complementary electronic and structural information, which allows the determination of the oxidation state of the X-ray absorbing metal atom and precise determination of distances between the absorbing metal atom and the protein atoms that surround it. Time-dependent XAS provides insight into the lifetimes and local atomic structures of metal-protein complexes during enzymatic reactions on millisecond to minute time scales, (a) The drawing describes a conventional stopped-flow machine that is used to rapidly mix the reaction components (e.g., enzyme and substrate) and derive kinetic traces as shown in (b). (b) The enzymatic reaction is studied by pre-steady-state kinetic analysis to dissect out the time frame of individual kinetic phases, (c) The stopped-flow apparatus is equipped with a freeze-quench device. Sample aliquots are collected after mixing and rapidly froze into X-ray sample holders by the freeze-quench device, (d) Frozen samples are subjected to X-ray data collection and analysis.

Electrodes of 2%-thoriated tungsten are the most frequently used water-cooled nonconsumable electrodes. Water-cooled copper anodes have been widely used in experimental work. Figure 1 shows a typical plasma jet assembly. A reactor chamber may be of any configuration desired to accommodate different feeding and quenching devices. 

Figure 8.43 Rapid Quench Device. Biocatalyst E and substrate S are combined in a mixing zone (hatched area) and the mixture ejected along a common outlet tube in order to be combined with quencher Q in another mixing zone. Different mixing times correlate with different reaction times t pre-quenching. Spectroscopic monitoring as a function of t gives first order relaxation curves for analysis.

Rapid-Mixing or Stop-Flow Monitoring To elucidate the mechanism of very fast enzyme reactions, it is critical to monitor the initial events before the system has a chance to attain a steady state. In many cases, the intermediate transient species exist for only few milliseconds. The fast enzyme reactions can be monitored readily by combining rapid mixing and quenching devices with mass spectrometry. The multiplex detection and fast scanning capabilities of time-of-flight (TOF) and Fourier transform (FT)-ion cyclotron resonance (ICR) mass spectrometers make them ideal for this combination. 

Figure 2. Rebinding of [ C]ADP to oxidized ( ) and DTT-reduced ( ) thylakoid membranes following 150 saturating flashes. After a dark interval of between 20 ms and 500s, samples were mixed with an equal volume of reaction medium containing 50 uM [ C]ADP, using a rapid quench device (Update Instruments). The reaction temperature was 4°C.

Y. Lin, et al.. Ultrafast Microfluidic Mixer and Freeze-Quenching Device. Anal. Chem., 2003, 75, 5381-5386. 

Tanaka M, Matsuura K, Yoshioka S, Takahashi S, Ishimori K, Hori H, Morishima 1 (2003) Activation of hydrogen peroxide in horseradish peroxidase occurs within approximately 200 micro s observed by a new fieeze-quench device. Biophys J 84 1998-2004... 

Another apparatus in which heat transfer is achieved by conduction to a solid substrate and one particularly appealing to polymo- studies is the piston and anvil quenching device. The design, shown in Fig. 12 and based on the principle of an accelerating substrate a inst a fixed globule was first conc v by Pietrokowsky (103). 

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